The AMChill packaged chiller, developed by natural refrigeration specialist KGM Refrigeration with support from Bitzer UK, runs on an ultra-low charge of ammonia, made possible by a new design that overcomes the need for a flooded evaporator.

Based on highly-reliable open-drive Bitzer W-series compressors optimised for use with ammonia, the chiller is designed for roof-top mounting without the need for expensive risk mitigation measures, such as high capacity exhaust ventilation, required in plant room applications.

The chiller's light weight and compact dimensions (1m wide by 1.6m long and 1.9m high) enable it to be easily transported onto rooftops without the use of a crane via a standard lift, saving installation time and cost.

Amar Marwaha, Engineering Director at KGM Refrigeration Ltd, said: 'From a thermodynamic perspective, ammonia is the most efficient refrigerant available, delivering very high energy efficiency and low running costs. As a natural refrigerant, its environmental credentials are also impeccable, having zero global warming potential and zero ozone depletion potential.'

Amar Marwaha added: 'Traditionally, ammonia's downsides are obviously toxicity and flammability. However, we went back to the drawing board to develop a new chiller design that dramatically reduces the charge required for a given duty, while retaining the efficiency and environmental benefits.'

Charge reduction is key to the chiller's innovative design. Flooded evaporators on conventional ammonia chillers require a large reservoir of liquid ammonia. The new chiller works with very low superheat, maximising efficiency.

This approach, coupled with minimised pipework, reduces the ammonia charge by around 75%. For example, for a duty of 150kW, the charge on a traditional ammonia chiller with flooded evaporator could be around 40kg, compared to just 10kg on the KGM chiller.

In addition to the roof-top mounted design, safety is further enhanced by the use of integrated ATEX-rated leak detection with system shutdown, and an ATEX-rated fan for enclosure ventilation.

'Ammonia plant obviously requires a specialist skill-set to install and service. The UK has a long heritage in ammonia refrigeration and retains a highly trained skills base, making it an attractive and viable solution from the get-go.'

The chiller is available in three sizes, spanning capacities from 100kW to 150kW (based on an outlet temperature of +6°C), and is ideal for use in pharmaceutical and industrial process cooling, cold stores, plastics manufacturing and for cooling industrial machine tools.

Pharmaceutical application 

A UK pilot project at a major pharmaceutical manufacturing site has proved the chiller’s performance and reliability. Sterling Pharma Solutions installed a 150kW ultra-low-charge AMChill packaged chiller at its site in Cramlington, to provide supplementary cooling for existing process refrigeration plant.

The pilot is part of a wider environmental programme by Sterling aimed at achieving carbon neutral status for the site. Other initiatives include the completion of a new anaerobic digestion plant to create methane gas from waste solvents, which is then converted into energy and injected into the national grid, and a combined heat and power (CHP) plant to generate the site’s own electricity for its manufacturing, laboratory and office spaces.

'The cooling load at the test site is highly variable, and provided excellent validation of the chiller's ability to respond rapidly to changes in demand,' said Amar Marwaha. 'To date, the unit has over 5,000 run hours, and has performed to design since being commissioned.'

Brian Peutherer, Vice President of Environment, Health and Safety at Sterling, said: 'Sterling was delighted to participate in the pilot trial, as innovative technology fits directly into our business model, and this was a great opportunity to apply it to our sustainability drive.

“We have set ourselves challenging environmental goals to become carbon neutral and achieve best-in-class energy, sustainability and waste management practices across our operations. Refrigeration is a key element. With zero global warming potential and zero ozone depletion potential, plus excellent efficiency, ammonia cooling systems are highly sustainable and future-proof against F-gas changes.”

He added: “Moreover, the new KGM chiller combines this with an ultra-low ammonia charge, packaged design and roof-top mounting, ensuring potential risks are minimised. Overall, our tests have shown that it delivers a superb optimum solution.'

On the basis of the successful trial, the company is installing further AMChill ultra-low-charge ammonia chillers at the site, and extending the roll-out to other production facilities.

Energy efficiency

One of the keys to the chiller’s outstanding efficiency is the use of a variable speed drive linked to a synchronous reluctance IE5 motor, believed to be the first refrigeration application in the UK of this state-of-the-art technology.

Linked to Bitzer's open-drive reciprocating compressor, it can modulate speed and enable output to be precisely matched to cooling load across a broad range of conditions.

This delivers a significant improvement in energy efficiency performance against conventional chillers running on synthetic refrigerants. For example, for a cooling output of 150kW at a typical duty point (+12°C/+6°C evaporator and +30°C/+35°C on the condenser), the AMChill chiller has a COP/EER of 5.43 compared with 4.95 for a similar unit running on R-513a, an improvement of around 10%.

A heat pump version of the chiller is also available to enable recovery of waste heat, further boosting overall efficiency levels.

KGM says it is now working on further reducing the ammonia charge by refining the design and minimising pipe lengths, which it believes could yield an additional 20% reduction – to around 8kg for a 150kW unit.

Benefits for end users and installers

For end users, the chiller's higher capital cost is more than offset by its extended working life (between 20-25 years) and lower energy costs, reducing the lifetime cost of ownership compared with standard chillers.

For installers, the benefits include compactness, ease of handling on site, and a packaged design that requires only water and electrical connections, making it 'plug and play'.

The Bitzer compressors at the heart of the system are supported by Bitzer AWA valves and high performance coalescing oil separator to minimise oil carry over, ensuring peak performance and system longevity.

Amar Marwaha said: 'We specified Bitzer units because of their high quality design and time-proven engineering. When people see a Bitzer compressor on a chiller, the quality speaks for itself”.

He added: 'Bitzer K’s Kevin Glass and James Graham have been highly supportive throughout the research and development process. As well as technical advice, this included a wider perspective on the requirements across Europe, which has been invaluable.'

Kevin Glass, managing director of Bitzer UK, said: 'We are delighted to support KGM Refrigeration's pioneering initiative. We as an industry, and indeed the world in general, face some difficult decisions in the light of the recently revised F-gas regulation. Rooftop-mounted, ultra-low charge packaged ammonia chillers offer some compelling benefits, and could well find application in mainstream applications currently served by global warming synthetic refrigerants.'